1. Field of the Invention
The present invention relates to a photosensitive composition capable of recording a volume hologram, a volume hologram recording medium using the above-described composition, and a volume hologram prepared using the relevant recording medium.
The present invention relates to a photosensitive composition for forming a volume hologram applicable to, for example, a graphic art (GA), a security card and optical elements (HOE) such as a color filter, a reflection plate for display, a head-up display or the like, and a photosensitive medium for recording a volume hologram using the above-described composition.
2. Description of the Related Art
Conventionally, a medium recording three dimensional information of an objective as an interference fringe by causing the difference of a refractive index inside of the recording layer using the light irradiating onto the objective and the reference light has been known as a volume hologram. In recent years, a photosensitive composition for recording a drying developing type volume hologram in which a wet development processing is not needed and capable of being mass-produced in the manufacturing of a volume hologram has occupied the attention.
As a photosensitive composition for manufacturing such a volume hologram, the product of Omnidex series of I.E. du Pont de Nemours and Company is the only one product commercially available on the mass-production level. Although this material is mainly made of a radical polymerization monomer and a binder polymer, a photo-radical polymerization initiator and a sensitizing pigment, it utilizes the difference of refractive indices between a radical polymerization monomer and a binder polymer. Specifically, when the relevant photosensitive composition formed in a film shape is exposed to the interferential light, the radical polymerization is initiated at the regions where the light strongly irradiates, and accompanying with it, the concentration gradient of the radical polymerization monomer is made, and the diffusion shift is occurred from the regions where the light weakly irradiates to the regions where the light strongly irradiates. As a result, sparse and dense portions of the radical polymerization monomer are made, and this appears as the difference of the refractive indices. This material system has the best performance as a photopolymer for volume hologram reported at present, the refractive index modulation amount Δn calculated by Kogelnik theory achieves to the order of 0.06 at maximum. However, the relevant Omnidex series (trade name) are weak at heat, and since these are colored, there is a limitation for the use of optical materials.
Moreover, a material system using a radical polymerization and cationic polymerization in combination has been reported. For example, Japanese Patent No. 2,873,126 discloses a system using a monomer having diallyl fluorene skeleton as a radical polymerization monomer having a high refractive index and a cationic polymerization monomer whose refractive index is smaller than that of the relevant a radical polymerization monomer. In this system, a component having a high refractive index is polymerized by radical polymerization at the time when it is exposed for forming the hologram, the radical polymerization monomer is diffused and shifted to the regions where the light irradiates, and the difference of the refractive indices is subsequently caused and the interference fringe is formed in accordance with a concentration distribution of the radical polymerization monomer, then the image is fixed by cationic polymerization with fixing exposure.
Moreover, a material system utilizing cationic polymerization has been disclosed, for example, in U.S. Pat. No. 5,759,721 and the like. Although there is an advantage in this material system that oxygen inhibition in the radical polymerization system does not exist, the photospeed of the cationic polymerization is slow, and there is also a problem that it is difficult for it to have the sensitivity to the long wavelength region.
Moreover, in Japanese Patent No. 2,953,200, an organic-inorganic hybrid material system for volume hologram using inorganic matrix network and photo-induced polymerization monomer in combination has been disclosed. In this system, an organic polymer invades into a rigid inorganic matrix network, the hologram recording medium is too rigid, and rolling in as a film becomes difficult, the processing appropriateness is bad, and there is a problem that a long time is needed at the time when forming a coating film. Moreover, since the affinity between an inorganic binder and an organic monomer is not good, there is also a problem that it is difficult to prepare a uniform coating material.
In the same as above Japanese Patent No. 2,953,200, that the flexibility is given to the inorganic binder by introducing an organic group in the inorganic matrix network, whereby the fragility of the hologram recording film is improved has been disclosed. However, in the same as above Japanese Patent No. 2,953,200, only that an organic group is introduced into the inorganic network by performing the hydrolysis and polycondensation polymerization of an organometallic compound having organic portion in side chain or an organometallic compound having a functional group capable of polymerizing with an organic monomer has been disclosed. Specifically, according to the disclosure of the same as above Japanese Patent No. 2,953,200, the network structure itself of the inorganic network is consisted of chains in which inorganic compounds are bonded each other, since the organic group is only introduced into the network structure of the inorganic network as a side chain in a pendant shape, it is not the one that essentially changes the rigid structure of the inorganic network.
Moreover, in Japanese Patent Application Laid-Open No. 2000-508783, the material in which metal ultra-fine particles are dispersed in the solid matrix as a hologram recording material has been disclosed, however, it is necessary to make the matrix fluidity and there has been a problem that the solid property is bad.
Moreover, as a material for volume hologram excellent at heat resistance, in Japanese Patent No. 3,075,081, hologram materials including a thermosetting epoxy oligomer, an aliphatic monomer capable of being radically polymerized, a photo-induced initiator for generating a radical species, a photo-induced initiator for activating cationic polymerization and a sensitizing pigment have been disclosed. However, the Value Δn of the volume hologram according to the relevant gazette is not so satisfied.
A variety of material systems have been disclosed in order to form a volume hologram recording film, however if the applications to the wide range of fields such as optical element and the like are considered, it is not sufficient, it is desired for a material system to sufficiently satisfy not only the hologram recording performances such as difference of refractive indices, sensitivity, transparency and the like, but also a variety of performances including physical properties such as heat resistance, film strength, environmental resistance, mechanical strength, flexibility, processing appropriateness, coating compatibility and the like.